Not applicable.
1. Field of the Invention
The present invention relates generally to disk drives, and in particular to a disk drive including a disk clamp with non-symmetric engaged fastener holes and a disk drive with non-uniformly torqued fasteners engaged with the disk clamp.
2. Description of the Prior Art
The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes the disk drive base, a cover, at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA).
The spindle motor includes a spindle motor hub that is rotatably attached to the disk drive base. The spindle motor hub has an outer hub flange that supports a lowermost one of the disks. Additional disks may be stacked and separated with annular disk spacers that are disposed about the spindle motor hub. A disk clamp is affixed about the spindle motor hub. Fasteners, such as screws, are disposed through fastener holes of the disk clamp and engage fastener openings that are circumferentially spaced about a periphery of the spindle motor hub for applying a clamping force by the disk clamp against the topmost disk to secure all of the disks to the spindle motor hub. The spindle motor typically includes a spindle motor base that is attached to the disk drive base. A shaft is coupled to the spindle motor base and the spindle motor hub surrounds the shaft. The spindle motor hub may be rotatably coupled to the shaft, and therefore the spindle motor base, typically via a pair of bearing sets. A stator is positioned about the shaft and is attached to the spindle motor base. A magnet element is attached to the hub flange. The stator includes windings that selectively conduct current to create a magnetic field that interacts with the various poles of the magnet element. Such interaction results in forces applied to the spindle motor hub that tend to rotate the spindle motor hub and the attached disks.
The head stack assembly has an actuator assembly having at least one head or slider, typically several, for reading and writing data to and from the disk. The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached sliders are moved relative to tracks disposed upon the disk.
The head stack assembly includes the actuator assembly and a flex circuit cable assembly that are attached to the actuator assembly. A conventional xe2x80x9crotaryxe2x80x9d or xe2x80x9cswing-typexe2x80x9d actuator assembly typically comprises an actuator body, a pivot bearing cartridge, a coil portion that extends from one side of the actuator body to interact with one or more permanent magnets to form a voice coil motor, and one or more actuator arms which that extend from an opposite side of the actuator body. The actuator body includes a bore and the pivot bearing cartridge engaged within the bore for allowing the actuator body to rotate between limited positions. At least one head gimbal assembly (HGA) is distally attached to each of the actuator arms. A head gimbal assembly includes a head for reading and writing data to and from the disks. In this regard, the actuator assembly is controllably rotated so as to move the heads relative to the disks for reading and writing operations with respect to the tracks contained on the disks.
The above described disk clamp arrangement for securing the disks gives rise to certain problems associated with the clamping force of the disk clamp and the thickness and strength of the disk clamp and disks. It is contemplated that the fasteners each include a fastener head that engages the disk clamp at the fastener holes. Fastener shanks extend from the fastener heads through the fastener holes of the disk clamp and engage the spindle motor hub. A majority of the clamping force applied to the disks is concentrated at locations immediately radially adjacent to the fastener holes. A measurably less amount of clamping force is applied to those portions of the disks at angular positions between the fastener holes. The clamping force as applied to the disks is observed to be sinusoidal in nature with peak values commonly occurring immediately radially adjacent the fastener holes and minimal values commonly occurring at positions intermediate adjacent ones of the fastener holes. This variation in clamping forces can cause the disks to become mechanically distorted in a repeating manner angularly about the disks.
Distortion of the disks from an ideal flat condition leads to a phenomenon referred to xe2x80x9crepeatable run-outxe2x80x9d associated with an undesirable modulation of read/write signals detected and produced by the heads of the disk drive. Accordingly, there is a need in the art for an improved disk drive in comparison to the prior art.
An aspect of the invention can be regarded as a disk drive that includes a disk drive base and a spindle motor hub rotatably coupled to the disk drive base. The disk drive further includes a disk disposed about the spindle motor hub and including a disk surface. The disk drive further includes a plurality of fasteners. The disk drive further includes a disk clamp attached to the spindle motor hub in mechanical communication with the disk surface for securing the disk. The disk clamp includes a plurality of engaged fastener holes formed through the disk clamp and non-symmetrically distributed about an axis of rotation. The engaged fastener holes are sized and configured to respectively receive the fasteners. The fasteners are engaged within the engaged fastener holes for attachment of the disk clamp and the disk to the spindle motor hub.
According to various embodiments of the present invention, the engaged fastener holes may be radially uniformly disposed from the axis of rotation. In another arrangement, the engaged fastener holes may be radially non-uniformly disposed from the axis of rotation. The engaged fastener holes may each be disposed a radial distance from the axis of rotation within ten percent of a nominal radial distance of all of the engaged fastener holes from the axis of rotation. The engaged fastener holes may be disposed angularly non-uniformly about the axis of rotation. Adjacent pairs of the engaged fastener holes may each be disposed an angular distance with respect to the axis of rotation within fifteen percent of a nominal angular distance of all of the engaged fastener holes with respect to the axis of rotation. The spindle motor hub may include a plurality of threaded fastener openings aligned with the engaged fastener holes of the disk clamp for respectively engaging the fasteners for attachment of the disk clamp to the spindle motor hub.
Another aspect of the invention can be regarded as a disk drive that includes a disk drive base and a spindle motor hub rotatably coupled to the disk drive base. The disk drive further includes a spindle motor hub rotatably coupled to the disk drive base. The spindle motor hub includes a plurality of threaded fastener openings. The disk drive further includes a disk disposed about the spindle motor hub. The disk drive further includes a disk clamp attached to the spindle motor hub for securing the disk. The disk clamp includes a plurality of engaged fastener holes formed through the disk clamp and aligned with the fastener openings of the spindle motor hub. The disk drive further includes a plurality of fasteners respectively disposed through the engaged fastener holes for attaching the disk clamp and disk to the spindle motor hub. The fasteners are non-uniformly torqued within the fastener openings for applying a non-symmetric clamping force by the disk clamp against the disk.